This invention relates to a control system for apparatus used in cereal milling plants.
The invention finds particular application in a mill for producing flour, more particularly baking flour, semolina and medium ground flour in a series of progressive stages.
Modern cereal mills are largely automatic. The heart of the mill, i.e. the milling portion, and more particularly the mill rolls and the cleaning installations are interconnected and actuated via electrical interlocking to such an extent that operation during the starting, operating and output phase can be regarded as completely automatic. The entire stream of product, starting from the raw grain, is automatically conveyed through all the milling stages.
White flour which is one of the main objectives of cereal milling must have a very low ash content. A low ash or husk content is directly contrary to maximum recovery of the endosperm. A large number of factors, e.g. the feel of the flour, the baking properties, taste and smell of the bread, are checked and constantly monitored by the miller and his laboratory assistants, using in many cases their own unaided senses. The reliability of the individual machines, mechanical conveying elements, actuating means, etc. has now been brought to such a high standard that a single man (i.e. the miller or head miller) can without aid, monitor a large mill with a daily output of some 300-400 tonnes.
In recent times, many proposals have been made for further automation of mills. The most obvious idea of all would be simply to control the mill by a computer. However, a single miller is still required. As a result the computer, with the necessary computer expert, is a retrograde step, and likely to lead to over-control of the mill and may endanger the present high level of automation as faults in the computer result in complete shut down of the plant. Although laboratory work has been going on for almost two decades, the computer has not been accepted in milling practice, except for "book-keeping" tasks, where it only collects the necessary information and processes or stores it for accounting and other book-keeping purposes. A yield computer is an example of the book-keeping computer. A yield computer is arranged to continuously monitor the weights of raw flour supplied and the products obtained therefrom, i.e. medium ground flour, bran, etc. from which it calculates the yield for a particular time or from a given load. Mill experts have not so far accepted a central control computer to supervise a mill because they know only too well that it may fail, resulting in complete shut down of the mill.
An important concept in the background of the invention is that a cereal mill should be treated in a manner appropriate to itself and not like a chemical factory or cement factory. animals will not accept fodder except in a form which appeals to them, and the same applies even more to man in his acceptance of flour. A purpose of the mill, therefore, must be to produce flour which meets the needs for baking good bread or for making good paste products. For this, however, the intervention of the miller with his skill and experience is essential. Accordingly an acceptable end product can be obtained only by full co-operation between the miller and the machinery.
One interesting discovery is that a mill must be piloted somewhat in the manner of a modern passenger aircraft. A mill must have an automatic "pilot" which helps the real pilot or miller without replacing him. In both the aircraft and the mill, the "take-off", "flying" and "landing" process must be assisted, but the head miller remains responsible for active guidance and piloting in a supervisory capacity, adding his own perception to the control of the mill process. He must, with his unaided senses, allow for all the important factors, more particularly those which are difficult to measure mechanically but which are critical in the process, and he must be able to give suitable control instructions at any time.